Talk to Izzay Meestere. He will make sure that you are really committed to betraying Freeport, then transport you to an instanced version of the Freeport Milita House. If you have a mercenary they will be suspended while inside this zone.

Go up the stairs to the second floor, then range pull the mobs one at a time to the stairs landing until you can get to the Commandant.

All the information I've helped gather has pinpointed the cache to the "big house." That must mean the Militia building. Most of the guards will be drawn away, leaving the building staffed by trainees. The cache will be locked away with its key held by the Commandant of the facility. While I'll be supported by two other squires, their jobs are already assigned and I'm the one who'll need to get the key, release the prisoners and take care of the cache.

Stage 1

I need to take down the Militia Commandant to obtain the key that will give me access to the lowest area of the building. That's where I'll find the prisoners and the main body of the weapons cache.

Start:

The Commandant is somewhere in the Militia building, just waiting for me to get the key.

Complete:

I've obtained the key.

The Commandant graciously gave me the key.

Stage 2

I must destroy the upstairs supplies, release the prisoners and destroy the weapons cache.

Start:

I must get an explosive device from the Squire at the entrance and place the first device upstairs.

Complete:

I've taken care of the upstairs area.

Start:

I need to free the prisoners in the holding cells.

Complete:

I've freed the prisoners.

Start:

I need to get another explosive device from the Squire at the entrance and place it inside the armory.

Complete:

I've blown up the cache!

I have destroyed the upstairs supplies, released the prisoners and destroyed the weapons cache.

Stage 3

I need to return to the main hall and escape with the other squires.

Start:

The other squires and I need to get out of the Militia building before we're discovered.

Complete:

I have been caught by Freeport and exiled!

I've made it back to the main hall...

While I was able to free the prisoners and destroy the weapons cache at the Militia building, something unexpected has happened.